This invention relates to an RF (radio frequency) power amplifier for a radio transmitter, a transmitter in a wire communication system using an RF signal, or other apparatus.
Recently, down-sizing has been advanced in portable radio telephone devices and automobile telephone devices. These telephone devices can communicate with a base station via an RF signal. Thus, the telephone devices include RF power amplifiers. Smaller-size RF power amplifiers are advantageous in further advancing down-sizing of the telephone devices. Generally, the RF power amplifiers of the telephone devices have an additional function of controlling the level of the power output in accordance with an instruction from the base station.
As will be explained later, prior-art RF power amplifiers have some problems.